Intermediate drill stem

ABSTRACT

Intermediate drill stem includes an alloy steel body of smaller inner diameter than usual for drill pipe machined to drill pipe outer diameter except having one or more integral protectors of larger outer diameter at intervals along its length and except further having integral transition portions of somewhat larger than drill pipe outer diameter near its ends and portions of elevator shoulders at the ends, the ends also being built up externally and internally with weld metal to match the wall thickness of extra long alloy steel connector members rod welded to the ends of the body. Typically the body of the intermediate drill stem is made from a worn out drill collar and if the ends of the collar are not too far gone the original integral drill collar connectors can be used. New material may be used for the body and if anticipated loading is not too great carbon steel could be used instead of alloy steel. In any case, the integral protectors could be omitted.

iJite States Patent 1191 Chance et a1.

INTERMEDIATE DRILL STEM Inventors: Glenn G. Chance; Sam T. Crews,

both of Houston; Clenis E. Wilson, Spring, all of Tex.

[73] Assignee: Smith International, Inc., Midland,

[22] Filed: May17, 1971 [21] Appl. No.: 143,953

Simonin 64/1 Jan. 8, 1974 5 7 ABSTRACT Intermediate drill stem includesan alloy steel body of smaller inner diameter than usual for drill pipemachined to drill pipe outer diameter except having one or more integralprotectors of larger outer diameter at intervals along its length andexcept further having integral transition portions of somewhat largerthan drill pipe outer diameter near its ends and portions of elevatorshoulders at the ends, the ends also being built up externally andinternally with weld metal to match the wall thickness of extra longalloy steel connector members rod welded to the ends of the body.Typically the body of the intermediate drill stem is made from a wornout drill collar and if the ends of the collar are not too far gone theoriginal integral drill collar connectors can be used, New material maybe used for the body and if anticipated loading is not too great carbonsteel could be used instead of alloy steel. In any case, the integralprotectors could be omitted.

25 Claims, 7 Drawing Figures 1 INTERMEDIATE DRILL STEM BACKGROUND OF"THE INVENTION a. Field of the Invention The invention pertains tointermediate drill stem placed between the drill collars and drill pipeof a drill string used in the rotary system of drilling holes in theearth, e.g. oil wells. Intermediate drill stem provides a gradualtransitiion between the rigid drill collar part of the drill string andthe flexible drill pipe part of the drill string. Intermediate stemresembles drill pipe in that the outer diameter is the same as that ofdrill pipe so as to fit drill pipe elevators, and the polar moment ofinertia of the crosssectional area of the connectors is larger than thatof the body, so that the connections are more rigid than the body andmost of the flexing takes place in the body and the connections need notbe made up as tight as for drill collars to prevent the shoulder sealfrom opening up under load. On the other hand intermediate stemresemblesdrillcollars in that it is run in compression to put weight onthe drill bit and the inner diameter is close to that of drill collars,providing a thick wall for weight, wear and strength. Body rigidity ofintermediate stem is intermediate that of drill pipe and drill collars.

B. Description of the Prior Art Prior workers in the art have tried outintermediate stem made by flash welding the necked down ends ofconventional drill pipe tool joints to a body made of heavy wall pipe.In this construction the body wasnot machined from drill collar stockand did not include any protector to prevent wear of the body caused byflexure into contact with the side of the earth bore. The tool jointconnectors were of conventional length and not adapted for remachiningwhen worn, it being contemplated that the body would wear out before thetool joints. Only a small number of lengths of such intermediate stemcould be used due to the excessive wear on the lowermost lengths wherethe compression loading and flexure are greatest. I

SUMMARY OF THE INVENTION The principal object of the invention is toprovide an intermediate drill stem that has a longer life thanpreviously known intermediate drill stem. This is accomplished by theprovision of an alloy steel body with one or more protectors integrallyformed along its length and with the connectors at each end, especiallythe pin end, having great length.

The protectors intermediate the connectors and the connectors both keepthe body of the intermediate stem out of contact with the well wallimmediately adjacent to the connectors and the protectors, therebyreducing waer on the body. The protectors and connectors both act ascentralizers so that by use of protectors the laterally unsupported bodylength between centralizers is reduced. The reduction may be to thepoint where the product of the unsupported body length and the bendingdeflection per unit lengthund'er expected lood will be less than thedifference between hole radius and body radius, thereby. keeping thebody out of contact with the well wall throughout its full length. Underordinary conditions one protector per usual thirty foot length ofintermediate stem accomplishes this result.

The use of extra long connectors aids in accomplishing the foregoingresult since they reduce the degree to which the connectors can cant inthe hole. A connection made up of pin and box connectors having acombined length (of maximum diameter portion) less than the holediameter can cant in the hole to an extent limited only by the pipeconnected thereto. Connector diameter is usually about 80 percent ofhole diameter so that to prevent such unlimited canting, the overallconnection length must be at least about 125 percent of the connectorouter diameter. However, to effectively limit canting and keep theconnection axis nearly parallel to or in alignment with the hole axis,the overall length of the maximum diameter portion should be muchgreater. According to the preferred embodiment of the invention theoverall pin and box connection length is from about 400 percent to 1,000percent of the outer diameter of the connectors.

As a result of the use of protectors and long connectors, the body maybe kept substantially out of contact with the well wall, thereby greatlyincreasing the life of the body. The use of high strength alloy steelfor the body keeps the bending stresses well below the yield strength ofthe body so that the number of cycles of flexure permissible prior tofatigue failure approaches infinity. To balance the connector life withthe long life of the body, the extra length of the connectors allows forremachining of the threads.

A further object of the invention is to provide an inexpensiveintermediate drill stem of the aforementioned type. To this end a wornout drill collar may be used for the body of the intermediate stern andthe connector members made of new drill collar stock, welded to thebody. The elevator shoulder is formed on the body rather than theconnector, so that the weld can be made between connector and body-endsof maximum thickness, thereby permitting the use of rod or bead typewelding and eliminating the need for expensive flash welding equipment.The inner surface of the body ends is built upwith weld metal to thesame diameter as the connector prior to being welded thereto.

In the process of welding the connector to the body, weld metal is builtup on the outside of the end of the body so that it is at least as largeas the connector. The elevator shoulder is formed at the built up end ofthe body of the intermediate stem. Adjacent the elevator shoulder thebody is provided with a transition portion of somewhat larger outerdiameter than the main part of the body so that there will be a gradualtransition in rigidity between the connectors and the main part of thebody to preventstress concentration at the weld. The connectors weldedto the ends of the body are long enough so that when added to the lengthof the worn out drill collar the resulting intermediate stem is longenough to stand in the usual racks and to reach up to the platform forworkers in the top of the drill rig, with enough length to spare so thatthe connectors can be cut back and remachined when worn down.

It is important to note that the body of the intermediate stem ismachined, whereby the protectors are formed integral with the bodywithout welding or upsetting, for any welding or upsetting, especiallyin an alloy steel body, can cause physical changes that alter thematerial whereby the intermediate stem might fail in use.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1, 2 and 2A are schematicfragmentary sectional views each showing intermediate stem in use in awell bore, FIG. 1 showing the prior art type of intermediate stem andFIG. 2 showing intermediate stem embodying the present invention;

FIG. 3 is an axial section through a new drill collar showing inshort-dashed lines the outline of a worn-out, stubbed drill collar andin heavy-dashed lines the outline of the body blank of an intermediatestem in accordance with the invention;

FIG. 4 is an axial section through the component machined body, andblank connector portions of the intermediate stem of FIG. 2 prior towelding together and machining of the connectors;

FIG. 5 is a schedule of typical dimensions and material specifications;

FIG. 6 is a composite enlarged fragmentary sectional view of thejunction of the body and a connector blank showing in the right handpart of the figure the body and blank after welding together and withthe weld supporting ring still in place prior to machining, the finishedouter diameter being indicated in dotted lines, the left-hand part ofthe figure showing the finished juncture; and

FIG. 7 is an axial section through a finished intermediate drill stemembodying the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1 there isshown a portion of a drill string, including several lengths 10 ofintermediate drill stem. Due to the compressive loading of theintermediate stem and the long unsupported length of the body it hasdeflected into contact with the low side of the well bore 11 at point12. The tool joints l3, 14, are also in contact with the well bore. Thecontact of the wall and stem body at point 12 causes excessive wear onthe body which results in its early failure. It is not necessary for thebody to wear completely through to fail, for due to the compressiveloading the wall of the pipe may buckle. The contact of the tool joints13, 14 with the well wall will cause wear of the boxes 14 whichultimately will result in failure of the tool joints.

Referring now to FIG. 2, there is shown a portion of a drill stringincluding several lengths of intermediate drill stem embodying theinvention. Due to compressive loading of the intermediate stem it hasflexed placing the protectors 21 in contact with the side of the wellbore 11. The connectors 22, 23 are also in contact with the well bore.The protectors 21 prevent wear on the smaller diameter portions of theintermediate stem. The high strength of the alloy steel body of the stemprovides a low stress ratio to resist fatigue. The long connectors 22,23 reduce canting, resist wear, and provide length for remachining ofthe threads as may be required due to the extra life of the stem.

Referring now to FIG. 3, there is shown a new alloy steel drill collarhaving a uniform outer diameter from end to end except for a threadedconnector pin 31 formed at one end. The inner diameter of the drillcollar is uniform from end to end except for a threaded connector box 32formed at the end opposite from the end at which the pin 31 is formed.

The dotted line outline in FIG. 3 shows the dimensions of the same drillcollar after it is worn out. The outer periphery 33 has worn downconsiderably and the inner periphery 34 is worn to a slightly largerdiameter than on the new collar. The box end of the drill collar hasseveral times been cut back and rethreaded at 32' so that the length ofthe drill collar has been reduced. The pin end of the drill collar hasseveral times been out back and remachined and finally a connector stub31' has been welded on at 39 and it too has several times been cut backand remachined so that the length of the drill collar has reduced at thepin end too. Although the pin end of the collar could be restubbed, thebox at the other end has such a thin wall that the connection would nolonger be strong enough, being likely to fail at the bottom 35 of thebox. Also, the pin shoulder 36 and box end face 37 are so small that themetal is apt to yield in compression if the pin and box are stressedenough in make up to prevent the pin shoulder to box end face contactarea from opening up when the connection is subjected to bending moment.The connection is thus likely to leak and fail through a washout. If thebox end of the drill collar were stubbed, the large outer diameter ofthe stub would soon wear down to the same diameter as the rest of thedrill collar; also, stubbing both ends would cost about the same asmachining a new drill collar. In short, the drill collar 30' is wornout. Because it is made of alloy steel it is not even useful asstructural steel since it must be perheated if it is to be weldedsuccessfully.

The heavy-dash outline in FIG. 3 shows the outline of the body blank ofalength of intermediate stem. The outer periphery 40 has been machineddown to drill pipe outer diameter, except at 41 which is left at thediameter 33 of the worn drill collar, thus forming an integral protectorfor the intermediate stem, and except further at the ends 42. Tocomplete the intermediate stem the connectors 31', 32' are cut off andnew alloy steel connectors the same size as connectors 31, 32 are weldedto the ends 42.

Referring to FIG. 4 there are shown the body blank 50 of theintermediate stem machined from the worn drill collar 30, and connectorblanks 51, 52 to be welded thereto. The outer peripheries 53, 54 of theconnector blanks are of full new drill collar diameter. The innersurfaces 55, 56 of the connector blanks are of the same inner diametersas a new drill collar. The ends of the body blank 50 and the adjacentends of the connector blanks are beveled slightly as shown at 57, 58,59, 60 to facilitate welding. The ends of the main body blank 50 arebuilt up interiorly with weld metal at 61, 62 to the same inner diameteras the connector blanks and machined smooth. The juncture of the weldmetal 61, 62 with the main body is tapered at 63, 64 (see also FIG. 5).

The lengths of the blanks 51, 52 are chosen so that together with thebody 50 taken from a worn drill collar the total length of theintermediate stem will be of the desired amount, e.g. 30 to 31 feet, thesame as the length of a new drill collar or drill pipe or intermediatedrill stem. The minimum length of the box connector blank is preferably15 inches for a 6% inch O.D. connector; the minimum length of the pinconnector blank for the same Giliis preferably winches {the extra threeinches allowing for cutting a new pin after the intermediate stem hasbeen in use so long that the original pin has worn out, while stillleaving about a foot of full diameter connector material. For example,assuming a length of 4% inch for the threaded portion of the pin, as isconventional for a six and one-half inch O.D. connector, the eighteeninch blank length provides for thirteen and one-half inches of maximumouter diameter portion. For 6% inch O.D. connectors, the minimum ratioof length to diameter of the maximum outer diameter portion of theconnectors is therefore 12/6.5 or 1.85 for the pin and l5/6.5 or 2.3 forthe box. The minimum length of the maximum outer diameter of thecombined pin and box connectors is thus about four (1.85 plus 2.3 equalstimes ther outer diameter of the connectors, as compared to a ratio ofabout three to one for a conventional tool joint connection. The maximumangle of cant is thus only 75 percent of that of an ordinary tool jointin an uncased hole.

For shorter lengths of body 50, the lengths of the connectors will beincreased, preferably as shown in the FIG. 5 chart, the lengths beingchosen so that there will be a relatively small number of differentsizes of connectors blanks to handle the full range of body lengths. Themaximum box connector should not exceed about two feet in length (an L/Dratio of 3.69 for a 6 /2 inch O.D. connector because otherwise the pintongs would be too high to be handled from the rig floor when the pipejoints are added or removed from the drill string. Therefore for themore common 25 foot body lengths resulting from fully worn out drillcollars,

the pin connector is three and one-half feet long compared to only twofeet for the box connector blank. A characteristic feature of thepreferred embodiment of the invention is thus a connector pin of greatlength, for example the length of the maximum outer diameter portion ofthe pin ranging approximately from 2 to 7 times the diameter of theconnector. The lower limit of approximately 2 is derived from the onefoot minimum length of maximum outer diameter portion of the pin and a6% inch O.D. connector as discussed previously (12 inch/6% inch 1.85).The upper limit of approximately 7 corresponds to a pin having a lengthof maximum outer diameter portion of 6% inch) (7) or 45% inch. Adding 4%inch for the threaded portion of the pin gives an overall pin length of50'inches or 4.2 feet. This is considerably longer than the greatest pinlength of 3% inch specified in FIG. 5, such a pin length correspondingto an L/D ratio of only (42 inch-4.5 ft. )/6.5 which equals 5.8.

From the pin max. O.D. length/diameter range ofl.85 to 7 and the boxlength/diameter range of 2.3 to 3.69, the range for the ratio oflengthto diameter of the maximum outer diameter portion of the combined pinand box connectors is therefore from 1,85 plus 2.3 4.15, or about 4, to3.54 plus 7 10.54 or about 10.

Although body blank 50 has been described as made from an old drillcollar, it could of course be machined from new stock having an outerdiameter equal to that of the protectors 41. If the protectors areomitted or made of smaller outer diameter and if a welding techniqueadapted to make a satisfactory weld with thinner material at the ends ofthe body where it joins the connectors is adopted, the new stock couldhave a smaller outer diameter. However, the outer surface 65 of the bodyof the intermediate stern will always be a machined surface, i.e. turnedin a lathe or milling machine, unless the integral protectors 41 areentirely omitted and the ends 42 omitted or formed by forging upsets onthe ends ofa bar or tube, in which latter case the surface 65 could be amill surface, i. e. extruded or rolled. A machined outer surface 65 istherefore a distinguishing characteristic of the preferred embodiment ofthe invention.

FIG. 5 specifies an AISI 4145H alloy steel for the connector blanks.This is the same type steel as for the body blank 50 in the usual casewhere the body is made from a worn out drill collar. Alloy steel may bedefined with reference to the A181 standards as comprising the A181 1300to 9900 range steels as distinct from the carbon steels in the A181 1000to 1200 range. See Marks Mechanical Engineers Handbook, Sixth Edition,pages 6-32 through 35 for a list of the compositions of the A181standard steels. Although the body 50 of the intermediate stem could bemade of carbon steel, e.g. in the case of new material, alloy steel ispreferred because of its greater strength since the intermediate stem isrun in compression. An alloy steel body is therefore a characteristic ofthe preferred embodiment of the invention. Preferably the yield strengthis at least 120,000 ps1.

Referring now to FIG. 6, there is shown the method of welding theconnector blanks to the body blank 50. The procedure is the same forboth the pin and box connector blanks so the procedure at only one endwill be described. The pin connector blank 51 is aligned concentricallywith body blank 50 by means of a generally exteriorly cylindricalsupport 70, which may be tubular or solid. The exterior of the supporthas an annular groove 71 which is positioned under the gap between theend of body blank 50 and the end of connector blank 51. The assembly ispreheated, e.g. in a furnace, and then the gap is filled with weld metalfrom a welding rod heated electrically or with a torch. As shown at 72the weld metal is built up beyond the outer periphery of the connectorand also overlapping the outer periphery of the end 42 as shown at 73.The end assembly comprising connector and transition portion is thenheated to relieve stresses resulting from welding. The outer peripheryof the connector, weld, and end are then machined down to the dottedline level 76, removing around one-sixteenth inch to one-eighth inchdepth of metal from the exterior of the connector, forming an 18 degreetaper elevator shoulder 77, and removing about one-eighth inch tothree-sixteenths inch depth of metal from the outer surface of end 42forming transition portion 78. By this process the ad versely heataffected metal at the surface of the connector and transition portionand weld are removed. The support is then bored out to the same innerdiameter as the inner periphery 79, of the connector, the bore extendingpast the built'up weld metal 62 inside the transition portion and thebevel 63 at its juncture with the inner periphery of the main body 50.Finally, the connector threads are machined.

As shown in FIG. 6, the outer diameter of the transition portions 78 isintermediate between the outer diameters of the main portion of the body50 or body blank 50 and residual portions 42' of the original ends 42 ofthe body blank.

Hard facing may be applied to the pin and box connectors and theprotectors, or any of them, if desired.

Referring now to FIG. 7 there is shown the finished intermediate drillstem including main body 50 of alloy steel having one or more integralprotectors 41 spaced apart along its length, transitionportions 78 atthe ends of the body and finished box and pin connectors 51', 52' ofalloy steel rod welded thereto by-welds 90, 91, with elevator shoulders77 adjacent to and including the welds.

As noted in the preceding paragraph, more than one protector may beemployed on a single length of intermediate stem. FIG. 2A illustratessuch a construction using two protectors 21. Otherwise, the constructionshown in FIG. 2A is the same as that of FIG. 2, previously described.

It is to be noted that although the body of the intermediate stem is ofsmaller outer diameter than the worn drill collar from which it is made,it still has a thick wall compared to drill collar. For example, thewall thickness may be three-fourths inch to twentyseven thirtieths inchfor 4% inch O.D. intermediate stem and seven-eighths inch to thirty-fivethirtysecondths inch for 5 inch O.D. intermediate stem, which isconsiderably thicker than that of drill pipe which ranges from aboutone-fourth inch to one-half inch. See pages 682 and 717 of the 6thedition of the Rotary Drilling Handbook, edited'by J. E. Brantly,published in 1961 by Parmer Publications, for the wall thickness ofvarious sizes of AP] standard drill pipe and drill collars. A wallthickness of about five-eighths inch may be considered as thedemarcation line between thick drill pipe and thin intermediate stem.

However, the body wall thickness is much less than that of theconnectors which have the same wall thickness as standard drill collars.Therefore even though the combined rigidity of the connectors is only afraction, e.g. 60 percent of that of the unthreaded portions thereof,even when fully made up with the unthreaded pin root and box mouth(about 1 inch long) in tension and compression, the rigidity of theconnector is still in excess of the rigidity of the main body of theintermediate stem.

That the foregoing is true will be apparent from consideration of aspecific example. Assume a balanced connection, as is preferable,wherein any flexure which takes place is evenly divided between the pinand box. To this end. for usual tapers (1.5 inch to 3 inches per foot)and usual lengths of threaded portions (2 inch to 4.5 inch), the polarsection modulus (1/C where 1 is the polar moment inertia and C is thedistance to the fibre carrying the greatest stress) of the box at theroot of the thread three-eighths inch toward the box mouth from the endof the pin when made up therein (hereinafter called the box bottom)should be 2% to 3%proferably 2% times the polar section modulus of thepin at the root of the thread three-fourths inch from the pin shoulder(hereinafter called the pin base). When such connections are properlymade up, e.g. according to the make up torque specifications given inthe Hughes Tool Company Section of the 1966-67 Composite Catalogue ofOil Field Equipment and Services at page 2558 for tool joints and onpage 48 of the 1963 edition of Rotary Shouldered Connections, publishedby Drilco Oil Tools, lnc., relative to drill collars, the intermediatestem being made up the same as for tooljoints, the box mouth and pinshoulder will not separate under normal loading. The box bottom istherefore the most flexible part of the connection.

The following table gives the polar moment of inertia of the body and ofthe connector box bottom for balanced connections of various sizes ofdrill pipe, inter-. mediate stem, and drill collars:

It will be seen from the foregoing table that the rigidity of the boxbottom of the intermediate stem is considerably in excess of that of thebody. It is a characteristic feature of intermediate drill stem inaccordance with the preferred embodiment of the invention that .therigidity of the body be considerably less than that of the connectors,i.e. less than that of the connector box bottom with balancedconnectors, so that flexure will take place primarily in the body ratherthan in the connectors, thereby prolonging the life of the connectors.This is a basic distinction from drill collars wherein the oppositeholds true.

Preferably, the connector rigidity is at least twice that of the body ofthe intermediate stem. This means that it is desired that the polarmoment of inertia of the box bottom of each connector box be at leasttwice the polar moment of inertia of the body of the intermediate drillstem. Since the polar moment of inertia is roughly directly proportionalto the fourth power of the outer diameter, the connectors should have anouter diameter of about (2)" or 1.2 times the diameter of the main bodyof the stem. For example, with a 5 inches outer diameter for the mainbody of the stem, the connectors should have an outer diameter of atleast 6 inches.

Since flexure takes place primarily in the body of the intermediate stemof the invention the thick walled alloy steel body with integralprotectors is most advantageous to prevent wear due to rubbing on theside of the well wall. In this regard it should be noted that to providelong wear, prevent cutting into the well wall, and to reduce canting,the protectors should have a length of at least about twice the outerdiameter of the protectors and should have tapered ends as shown at 92,93 in FIG. 7.

The protectors of the present invention are to be distinguished fromso-called drill pipe protectors used to prevent wear when drill pipe isrun inside casing. The latter are usually made of rubber. The protectorsof the present invention are made of metal and preferably have ahardness of at least 250 Brinell, e.g. 277-331 Brinell. They aremachined integral with the body of the intermediate stem whichdistinguishes them from various subsequently applied types of metaldrill pipe protectors. The hardness of the body of the stem ispreferably that of conventionaldrill collars, e.g. about 250 Brinell,preferably 277-331 Brinnell.

In order to be effective in keeping the main portion of the body of theintermediate stem out of contact with the well wall, the outer diameterof the protectors should be as large as possible compatible with otherdrilling requirements such as fluid flow between protector and wellwall. An outer diameter equal to that of the maximum outer diameterportion of the connectors would be preferable. However, since theprotector is to be integral with the body and the body formed bymachining down a tube of metal whose outer diameter from end to end isinitially the same as that of the protector, economy in material costsand machining time suggests that the protectors have a somewhat smallerDrill pipe Intermediate stem Drill collars Body O.D. fin.) 4% 5 4% 6 6%Connector O.D. (in.) 6 6% 6 6% 6 6% Body ID. (in.) 3.825 4.275 2 %a t0 32 to 3 2% 2% Body In 9. 14. 35 17.1 16.1 27. 6 25. 9 60. 7 76. 7Connector style 4%XH 5"XH 4IF(=4 XH).4%"IF(=5 XH) 4% PH 4 IF ConnectorIo at box bottom- 54.4 58 54.4 58 51.5 64.5 Ratio Ic/In 5.6 4.05 3.18 3.38 2.10 2. 24 0. 0. 84

outer diameter than the connectors if the body is made of new material.If the body is made of a worn out drill collar, the protector outerdiameter may be that of the worn out collar. Since a collar usuallybecomes worn out by the connector box outer diameter wearing down so farthat the box wall becomes too thin, a fairly definite minimum outerdiameter for the protector is established in this case. This turns outto be onehalf inch larger than the diameter of the main portion of thebody of the stem, which provides a one-fourth inch standoff distancebetween the main portion of the body! of the stem and the well walLThediameter of the protector preferably is initially at least one-half inchlarger than that of the main portion of the'body of the stem and mayrange up to as large as the diameter of the maximum outer diameterportion of the connectors.

- Whatever the initial diameter, as the intermediate stem is used theouter diameters of the protectors and connectors will become smaller.

The preferred minimum psacing between centralizers (connectors and/orprotectors)is about feet, to prevent body contact with well wall. it isto be observed that if the standoff distance of the protectors, i.e.difference between protector outer radius and that of the main portionof the body, is large, the spacing of the protectors along the length ofthe intermediate stem may be increased.

The connector hardness (e.g. above 250 Brinell, preferably 277 to 331Brinell), thread form, shoulder height, and distance from shoulder tothreads (e.g. one inch) is preferably that of conventional rotaryshouldered connectors for tool joints and drill collars.

Although the intermediate stem has been described as made by weldingconnectors to a body formed from either a worn drill collar or from newpipe, the connectors could also be formed integral with the body, e.g.from all new stock or by using the connectors of the worn drill collar.In the latter connection it is to be noted that a connector too worn tobe suitable for drill collars may yet be satisfactory for intermediatestem since the make up torque need not be as high and since the flexurewill take place primarily in the body of the intermediate stem ratherthan in the connection.

While a preferred embodiment of the invention has been shown anddescribed and several modifications thereof described, manyothermodifications can be made by one skilled in the art withoutdeparting from the spirit-of the invention.

We claim:

I. An intermediate drill stem comprising an elongated, tubular, steelbody the main portion of which has a substantially uniform outerdiameter, said body having a wall thickness 'of at least aboutfive-eighths inch in the main portion thereof.

a tubular alloy steel connector connected to each end of said body,

one of said connectors being interiorly threaded at its end oppositefrom its end that is connected to said body, said interiorly threadedend providing a box at one extremity of the stem, the other of saidconnectors having a portion of reduced outer diameter at itsend'opposite from its end that is connected to said body, said portionof reduced outer diameter being threaded to provide a pin at the otherextremity of the stem,

the maximum outer diameter portion of each of said connectors being atleast l.2 times that of said main portion of the body whereby therigidity of a connection comprising such pin and box connectors can betwice that of the main portion of the body of the stem,

said intermediate stem being distinguished by the length of the maximumdiameter portion of the pin connector being in the range of nearly twiceto about seven times the outer diameter of the connector,

the combined length of the maximum diameter portions of the pin and boxconnectors being in the range of four to ten times the outer diameter ofsaid maximum diameter portions,

the body of the stem being made of alloy steel having a yield strengthof at least about 120,000 psi,

the outer surface of said body being a machined surface,

said body having ends of larger outer diameter than that of said mainportion of the body but of somewhat smaller outer diameter than that ofthe maximum diameter portion of the connectors,

each connector being rod welded to one of said ends with the weld metaloverlapping the end to build up the maximum outer diameter of the end toequal that of the connector, and

a tapered elevator shoulder at each end of the body extending into saidbuild up of weld metal.

2. Subject matter of claim 1 further distinguished by:

the inner diameters of said connectors being equal to each other andslightly smaller than that of the main portion of said body,

the inner diameter of said body being uniform througout except at theends where the body is built up with weld metal on the inside to makethe ends have the same inner diameter as the connectors adjacent thewelds.

3. Subject matter of claim 2 further distinguished by:

said body having a transition portion between each end and the main bodyportion,

said transition portions each having an outer diameter smaller than thatof said ends and larger than that of said main portion of the body.

4. Subject matter of claim 3 further distinguished by:

said body having at least one portion located'between and spaced fromthe ends of the body which one portion has a larger outer diameter thansaid main portion of the body,

said portion of larger outer diameter being formed integral with saidmain portion of the body and providing a protector against wear on themain portion of the body.

5. An intermediate drill stem comprising an elongated, tubular, steelbody the main portion of which has a substantially uniform outerdiameter,

said body having a wall thickness of at least about five-eighths inch inthe main portion thereof,

a tubular alloy steel connector connected to each end of said body,

one of said connectors being interiorly threaded at its end oppositefrom its end that is connected to said body, said interiorly threadedend providing a box at one extremity of the stem,

the other of said connectors having a portion of reduced outer diameterat its end opposite from its end that is connected to said body,saidportion of reduced outer diameter being threaded to provide the endsof said protectors being tapered where they a pin at the other extremityof the stem,

the maximum outer diameter portion of each of said connectors being atleast 1.2 times that of said main portion of the body whereby therigidity of a connection comprising such pin and box connectors can betwice that of the main portion of the body of the stem,

said intermediate stem being distinguished by the length of the maximumdiameter portion of the pin connector being in the range of nearly twiceto about seven times the outer diameter of the connector,

the combined length of the maximum diameter portions of the pin and boxconnectors being in the range of four to ten times the outer diameter ofsaid maximum diameter portions,

the body of the stem being made of alloy steel having a yield strengthof at least about 120,000 psi,

the outer surface of said body being a machined surface,

said body having ends of larger outer diameter than that of said mainportion of the body but of somewhat smaller outer diameter than that ofthe maximum diameter portion of the connectors,

each connector being rod welded to one of said ends with the weld metaloverlapping the end to build up the maximum outer diameter of the end toequal that of the connector,

a tapered elevator shoulder at each end of the body extending into saidbuild up of weld metal,

the inner diameters of said connectors being equal to each other andslightly smaller than that of the main portion of said body,

the inner diameter of said body being uniform throughout except at theends where the body is built up with weld metal of the inside to makethe ends have the same inner diameter as the connectors adjacent thewelds,

said body having a plurality of protectors located between and spacedfrom the ends of the body each of which protectors has 'a larger outerdiameter than said main portion of the body,

said protectors being formed integral with said main portion of the bodyand providing protection against wear on the main portion of the body,

said protectors each having an outer diameter at least one half inchlarger than the outer diameter of the main portion of the body of thestem,

join the main portion of the body,

the length of each protector being at least twice the outer diameter ofthe connectors.

6. An intermediate drill stem comprising an elongated, tubular, steelbody the main portion of which has a substantially uniform outerdiameter,

said body having at least one portion located between said body having awall thickness of at least five- 6 eighths inch in the main portionthereof.

said body having ends of larger outer diameter than the main portion ofthe body, the outer diameter of said ends being substantially as largeas that of said protector,

a tubular steel connector rod-welded to each end of said body,

said connectors each having a larger outer diameter than the end of thebody to which it is welded, the weld metal overlapping the end to buildup its outer diameter to that of the connector.

7. An intermediate drill stem comprising an elongated, tubular, steelbody the main portion of which has a substantially uniform outerdiameter,

said body having a wall thickness of at least fiveeighths inch in themain portion thereof,

said body having at least one protector located between and spaced fromthe ends of the body,

said protector having a larger outer diameter than said main portion ofthe body,

said protector being formed integral with said main portion of the body,

said body having ends of larger outer diameter than the main portion ofthe body, the outer diameter of said ends being substantially as largeas that of said protector,

a tubular steel connector rod welded to each end of said body,

said connectors each having a larger outer diameter than the end of thebody to which it is welded, the weld metal overlapping the end to buildup its outer diameter to that of the connector,

a tapered elevator shoulder at each end of the body extending into saidbuild up of weld metal thereon.

8. Subject matter of claim 7 further distinguished by:

the inner diameters of said connectors being equal to each other andslightly smaller than that of the main portion of said body,

the inner diameter of said body being uniform throughout except at theends where the body is built up with weld metal on the inside to makethe ends have the same inner diameter as the connectors adjacent thewelds.

9. Subject matter of claim 7 further distinguished by:

the maximum outer diameter portion of each of said main portion of thebody whereby the rigidity of a connection comprising such pin and boxconnectors may be twice that of the main portion of the body of thestem,

said body having a transition portion between each end and the main bodyportion, said transition portions each having an outer diameter smallerthan that of said ends and larger than that of said main portion of thebody. l

10. Subject matter of claim 7 further distinguished the length of thebox connector being at least of the order of twice the outer diameter ofthe connector,

the length of the maximum diameter portion of the pin connector being inthe range of nearly twice to aboue seven times the outer diameter of theconnector.

11. An intermediate drill stem comprising an elongated, tubular, alloysteel body the main portion of which has a substantially uniform outerdiameter, the exterior surface of said main portion being a machinedsurface,

said body having at least one portion located between l3 and spaced fromthe ends of the body whi'ch one portion has a larger outer diameter thansaid main portion of the body, said portion of larger outer diameterbeing formed integral .with said main portion of the body and providinga protector against wear on the main portion of'the body, the ends ofsaid protector being tapered where they join the main portion of thebody, 7 said body having a wall thickness of at least fiveeighths inchin the main portion thereof, said body having ends of larger outerdiameter than the main portion of the body, the outer diameter of saidends being substantially as large as that of said protector, I said bodyhaving a transition portion between each end and the main body portion,said transition portions each having an outer diameter smaller than thatof said ends and larger than that of said main portion of the body, 4 atubular alloy steel connector ro'd welded to each end of said body, Isaid connectors each having a larger outer diameter than the end of thebody to which it is welded, the weld metal overlapping the end to buildup its outer diameter to that of the connector, a tapered elevatorshoulder at each end of the body extending into said build up of weldmetal thereon, the inner diameters of said connectors being equal toeach other and slightly smaller than that of the main portion of saidbody,

the inner diameter of said body being uniform throughout except at theends where the body is built up with weld metal on the inside to makethe ends have the same innerdiameter as the connectors adjacent thewelds, 7

one of said connectors being interiorly threaded at its end oppositefrom its welded end to provide a box at one extemity of the stem,

the other of said connectors having a portion of reduced outerdiameterat its end opposite from its welded end, said portion of reduced outerdiameter being threaded to provide a pin at the other-extemity of thestem,

the maximum outer diameter portion'of eachof said connectors being atleast 1.2 times that of said main portion of the body whereby therigidity of a connection comprising such pin and box connectors cay betwice that of the main portion of the body of the stem, i

the length of the maximum diameter portion of the pin connector being inthe range of. nearly twice to about seven times the outer diameter ofthe connector. 1

the combined length of the maximum diameter portions of the pin and boxconnectors being in the range of four to ten times theouter diameter ofsaid maximum diameter portions,

the length of each protector being at least of the same order ofmagnitude as the outer diameter of the protector,

each said protector having a diameter at least onehalf inch larger thanthat of said main portion of the body, .7

said connectors and each protector body providing centralizers for saidintermediate stem,

the longitudinal spacing between said centralizers being a maximum of 15feet.

14' 12. An intermediate drill stem comprising an elongated, tubular,steelbody the main portion of which has a substantially uniform outerdiameter. said body having a wall thickness of at least aboutfive-eighths inch in the main portion thereof,

a tubular alloy steel connector connected to each end of said body, oneof said connectors being interiorly threaded at its end opposite fromits end that is connected to said body, said interiorly threaded endproviding a box at one extremity of the stem, the other of saidconnectors having a portion of reduced outer diameter at its endopposite from its end that is connected to said body, said portion ofreduced outer diameter being threaded to provide a pin at the otherextremity of the stem, the maximum outer diameter portion of each ofsaid connectors being at least 1.2 times that of said main portion ofthe body whereby the rigidity of a connection comprising such pin andbox connectors can be twice that of the main portion of the body of thestem, said connectors being long axially compared to the diameterthereof, the combined length of the maximum diameter portions of the pinand box connectors being at least four times the outer diameter of saidmaximum diameter portions, the outer surface of said main portion ofsaid body being a turned machined surface, said body having ends oflarger outer diameter than that of said main portion of the body, eachconnector being welded to one of said ends, said body having at leastone portion located between and spaced from the ends of. the body whichone portion has a larger outer diameter than said main portion of thebody, said portion of larger outer diameter providing a protectoragainst wear on the main portion of the body, each said protector beinghomogeneously integral with said main portion of the body, saidprotector and main portion being one and the same single piece of metal,each said protector having an outer diameter at least one-half inchlarger than the outer diameter of the main portion of the body of thestem, the length of each protector being at least twice the outerdiameter of the connectors, said long connectors and eachsaid protectorbeing ing as centralizers for said intermediate stem.

13. Subject matter of claim 12, further distinguished by: V

said body having a transition portion between each end and the main bodyportion,

said transition portions each having an outer diameter smaller than thatof said ends and larger than that of said main portion of the body. 14.Subject matter of claim 12"further distinguished by:

the outer diameter of said ends of the body being substantially as largeas that of said protector, said connectors each having a larger outerdiameter than the end of the body to which it is welded, the weld metaloverlapping the end to build up its outer diameter to that of theconnector. 15. Subject matter of claim 14 further distinguished by:

spaced. apart along the length of the stern and servsaid body having atransition portion between each end and the main body portion, saidtransition portions each having an outer diameter smaller than that ofsaid ends and larger than that of said main portion of the body. 16.Subject matter of claim 14 further distringuished by:

said stem having an elevator shoulder at each end of the body at thejuncture'of said end and the weld, each shoulder including a portion ofthe metal of the weld and a portion of the metal of the end of the body.17. Subject matter of claim 16 further distinguished by:

said body having a transition portion between each end and the main bodyportion, said transition portions each having an outer diameter smallerthan that of said ends and larger than that of said main portion of thebody. 18. Subject matter of claim 12 further distinguished by:

the ends of said protector being tapered where they join the mainportion of the body, the longitudinal distance between the adjacentextremities of adjacent ones of said centralizers being not in excess ofIS feet. 19. Subject matter of claim 12, said connectors being free ofhard facing thereabout,

said protector being of smaller outer diameter than that of the maximumouter diameter portion of said connectors, I said protector having aband of hard facing material set in an annular groove around saidprotector. 20. Subject matter of claim 12 wherein said intermediate stemhas an inner diameter characteristic ofa drill collar and an outerdiameter characteristic of drill pipe.

21. An intermediate drill stem comprising an elongated, tubular, steelbody the main portion of which has a substantially uniform outerdiameter, said body having ends of larger outer diameter than that ofthe main portion thereof, a tubular alloy steel connector connected toeach end of said body, one of said connectors being interiorly threadedat its end opposite from its end that is connected to saidbody, saidinteriorly threaded end providing a box at one extremity of the stem,

the other of said connectors having a portion of reduced outer diameterat its end opposite from its end that is connected to said body, saidportion of reduced outer diameter being threaded to provide a pin at theother extremity of the stem,

the maximum outer diameter portion of each of said connectors being atleast 1.2 times that of said main portion of the body whereby therigidity of a connection comprising such pin and box connectors can betwice that of the main portion of the body of the stem,

each of said connectors being connected to one of said ends of the bodyby added weld metal joining the connector to the end,

each connector having a maximum outer diameter larger than the end ofthe body to which it is welded, the weld metal overlapping the end tosuch an extent as to build up its outer diameter to that of said maximumdiameter of the connector.

22. Subject matter of claim 21 said stem having an elevator shoulder ateach end of the body at the juncture of said end and the weld,

each shoulder including a portion of the metal of the weld and a portionof the metal of the end of the body.

23. Combination of claim 1 including the hereinbefore set forthinvention.

24. An intermediate drill stem comprising an elongated, tubular, alloysteel body the main portion of which has a substantially uniform outerdiameter,

said body having ends of larger outer diameter than that of the mainportion thereof,

said main portion having a wall thickness of at least about five-eighthsinch,

a tubular alloy steel connector connected to each end of said body,

one of said connectors being interiorly threaded at its end oppositefrom its end that is connected to said body, said interiorly threadedend providing a box at one extremity of the stem,

the other of said connectors having a portion of reduced outer diameterat its end opposite from its end that is connected to said body, saidportion of reduced outer diameter being threaded to provide a pin at theother extremity of the stem,

the maximum outer diameter portion of each of said connectors being atleast 1.2 times that of said main portion of the body whereby therigidity of a connection comprising such pin and box connectors can betwice that of the main portion of the body of the stem,

said connectors being long axially compared to the diameter thereof, thecombined length of the maximum diameter portions of the pin and boxconnectors being at least four times the outer diameter of said maximumdiameter portions,

the outer surface of said main portion of said body being a turnedmachined surface,

said body having ends of larger outer diameter than that of said mainportion of the body,

each connector being homogeneously integral with one of said ends of thebody, each said connector and body being made of one and the same pieceof metal,

said body having at least one portion located between and spaced fromthe ends of the body which one portion has a larger outer diameter thansaid main portion of the body, said portion of larger outer diameterproviding a protector against wear on the main portion of the body,

each said protector being homogeneously integral with said main portionof the body, said protector and main portion being one and the samesingle piece of metal,

7 each said protector each having an outer diameter at least one-halfinch larger than the outer diameter of the main portion of the body ofthe stem,

the length of each protector being at least twice the outer diameter ofthe connectors,

said long connectors and each said protector being spaced apart alongthe length of the stem and serving as centralizers for said intermediatestem.

25. Subject matter of claim 12,

said body being made of steel in the AIS]. l to 1,200 series. I

i 7 UNITED STATES PATIENT OFFICE cpn'riripara or connpcrion 3,7 4,28JANUARY '8, l 974 .i Patent No. 8 5 I Dated GLENN G CHANCE 53?? -T(IREWS s and CLENIS E WILSON Inventofls) It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below;

I r N! THE INTRODUCTION Item [2l], on the line following theiline "f2l]App] Moa 143,953"; insert;

g Related U. S ,."Ap pl ication Data [63] This application is a divisionof prior copending application, Serial No 825,,l09 filed May 1 1969, nowabandoned, which was copending with and a continuation-inpart ofourprior appl ication Serial No; 669,138 filed September 20, l967, nowabandoned, of which the present application is a continuation. "Ourpending application Serial No. l65,8l0 filed June '24, l97l is acontinuation of Serial N0- 825,lO9.,

"IN THE SPECIFICATION Colnm n' Line 2 in serti:

-- CROSS-REFERENCE ITORELATAED APPLICATION This application is adivision of prior copending application, Serial No. "825,109 .filed Mayl l969, now abandoned, which was copending with and a'continuation-in-part of our prior application'Serial No 669,l38 filedSeptember 20, 1967, now abandoned of which the present appl ication is acontinuation, Our pending application Serial No. 165,8l0 filed June 24l9 7l is a continuation of Serial No. .82 5,l-09.

e I Page 2 UNITED STATES PATENT OFFICE CERTIMC E @F CUECTIQN Patent No.8 ,238 Dated January eighth 197-4 Inventor) GLENN G. CHANCE, SAM T.CRENS AND CLENIS' E. WILSON It is certified that errom appears in theabove-identified patent and that said Letters Patent are herebycorrected as'shown below:

the cover sheet [73] "Smith International, .Inc. Midland, Pa." shomfldread-.- Smith lnternat'iona] Inc. Mid1and, Texas". Y

"Signed and sealed this 19th day .of Nqvember 1974.

(SEAL) Att'est I I MCCOY MI.'. .-;GIBIS ONIJR. v e "c; MARSHALL DANNAtte s'ting Officer I Commissioner of Patents Disclaimer 3,784,238.GlennG. Change and Sam T. Ua'ews, Houston, and Glands E. Wilson, Spring, Tex.INTERMEDIATE DRILL STEM. Patent dated J an. 8, 1974. Disclaimer filedNov. 30, 1973, by the assignee, Smith International, Inc. Herebydisclaims the portion of the term of the patent subsequent to Nov. 201990.

7 [Ofiicz'al Gazette Jane 25, 1974.]

1. An intermediate drill stem comprising an elongated, tubular, steelBody the main portion of which has a substantially uniform outerdiameter, said body having a wall thickness of at least aboutfive-eighths inch in the main portion thereof. a tubular alloy steelconnector connected to each end of said body, one of said connectorsbeing interiorly threaded at its end opposite from its end that isconnected to said body, said interiorly threaded end providing a box atone extremity of the stem, the other of said connectors having a portionof reduced outer diameter at its end opposite from its end that isconnected to said body, said portion of reduced outer diameter beingthreaded to provide a pin at the other extremity of the stem, themaximum outer diameter portion of each of said connectors being at least1.2 times that of said main portion of the body whereby the rigidity ofa connection comprising such pin and box connectors can be twice that ofthe main portion of the body of the stem, said intermediate stem beingdistinguished by the length of the maximum diameter portion of the pinconnector being in the range of nearly twice to about seven times theouter diameter of the connector, the combined length of the maximumdiameter portions of the pin and box connectors being in the range offour to ten times the outer diameter of said maximum diameter portions,the body of the stem being made of alloy steel having a yield strengthof at least about 120,000 psi, the outer surface of said body being amachined surface, said body having ends of larger outer diameter thanthat of said main portion of the body but of somewhat smaller outerdiameter than that of the maximum diameter portion of the connectors,each connector being rod welded to one of said ends with the weld metaloverlapping the end to build up the maximum outer diameter of the end toequal that of the connector, and a tapered elevator shoulder at each endof the body extending into said build up of weld metal.
 2. Subjectmatter of claim 1 further distinguished by: the inner diameters of saidconnectors being equal to each other and slightly smaller than that ofthe main portion of said body, the inner diameter of said body beinguniform througout except at the ends where the body is built up withweld metal on the inside to make the ends have the same inner diameteras the connectors adjacent the welds.
 3. Subject matter of claim 2further distinguished by: said body having a transition portion betweeneach end and the main body portion, said transition portions each havingan outer diameter smaller than that of said ends and larger than that ofsaid main portion of the body.
 4. Subject matter of claim 3 furtherdistinguished by: said body having at least one portion located betweenand spaced from the ends of the body which one portion has a largerouter diameter than said main portion of the body, said portion oflarger outer diameter being formed integral with said main portion ofthe body and providing a protector against wear on the main portion ofthe body.
 5. An intermediate drill stem comprising an elongated,tubular, steel body the main portion of which has a substantiallyuniform outer diameter, said body having a wall thickness of at leastabout five-eighths inch in the main portion thereof, a tubular alloysteel connector connected to each end of said body, one of saidconnectors being interiorly threaded at its end opposite from its endthat is connected to said body, said interiorly threaded end providing abox at one extremity of the stem, the other of said connectors having aportion of reduced outer diameter at its end opposite from its end thatis connected to said body, said portion of reduced outer diameter beingthreaded to provide a pin at the other extremity of the stem, themaximum outer diameter portion of each of said connectors being at least1.2 times that of said main portion of the body whereby the Rigidity ofa connection comprising such pin and box connectors can be twice that ofthe main portion of the body of the stem, said intermediate stem beingdistinguished by the length of the maximum diameter portion of the pinconnector being in the range of nearly twice to about seven times theouter diameter of the connector, the combined length of the maximumdiameter portions of the pin and box connectors being in the range offour to ten times the outer diameter of said maximum diameter portions,the body of the stem being made of alloy steel having a yield strengthof at least about 120,000 psi, the outer surface of said body being amachined surface, said body having ends of larger outer diameter thanthat of said main portion of the body but of somewhat smaller outerdiameter than that of the maximum diameter portion of the connectors,each connector being rod welded to one of said ends with the weld metaloverlapping the end to build up the maximum outer diameter of the end toequal that of the connector, a tapered elevator shoulder at each end ofthe body extending into said build up of weld metal, the inner diametersof said connectors being equal to each other and slightly smaller thanthat of the main portion of said body, the inner diameter of said bodybeing uniform throughout except at the ends where the body is built upwith weld metal of the inside to make the ends have the same innerdiameter as the connectors adjacent the welds, said body having aplurality of protectors located between and spaced from the ends of thebody each of which protectors has a larger outer diameter than said mainportion of the body, said protectors being formed integral with saidmain portion of the body and providing protection against wear on themain portion of the body, said protectors each having an outer diameterat least one-half inch larger than the outer diameter of the mainportion of the body of the stem, the ends of said protectors beingtapered where they join the main portion of the body, the length of eachprotector being at least twice the outer diameter of the connectors. 6.An intermediate drill stem comprising an elongated, tubular, steel bodythe main portion of which has a substantially uniform outer diameter,said body having at least one portion located between and spaced fromthe ends of the body which one portion has a larger outer diameter thansaid main portion of the body, said portion of larger outer diameterbeing formed integral with said main portion of the body and providing aprotector against wear on the main portion of the body, the ends of saidprotector being tapered where they join the main portion of the body,said body having a wall thickness of at least five-eighths inch in themain portion thereof. said body having ends of larger outer diameterthan the main portion of the body, the outer diameter of said ends beingsubstantially as large as that of said protector, a tubular steelconnector rod-welded to each end of said body, said connectors eachhaving a larger outer diameter than the end of the body to which it iswelded, the weld metal overlapping the end to build up its outerdiameter to that of the connector.
 7. An intermediate drill stemcomprising an elongated, tubular, steel body the main portion of whichhas a substantially uniform outer diameter, said body having a wallthickness of at least five-eighths inch in the main portion thereof,said body having at least one protector located between and spaced fromthe ends of the body, said protector having a larger outer diameter thansaid main portion of the body, said protector being formed integral withsaid main portion of the body, said body having ends of larger outerdiameter than the main portion of the body, the outer diameter of saidends being substantially as large as that of said protector, a tubularsteel connector rod welded to each end of said body, said connectorseach having a larger outer diameter than the end of the body to which itis welded, the weld metal overlapping the end to build up its outerdiameter to that of the connector, a tapered elevator shoulder at eachend of the body extending into said build up of weld metal thereon. 8.Subject matter of claim 7 further distinguished by: the inner diametersof said connectors being equal to each other and slightly smaller thanthat of the main portion of said body, the inner diameter of said bodybeing uniform throughout except at the ends where the body is built upwith weld metal on the inside to make the ends have the same innerdiameter as the connectors adjacent the welds.
 9. Subject matter ofclaim 7 further distinguished by: the maximum outer diameter portion ofeach of said connectors being at least 1.2 times that of said mainportion of the body whereby the rigidity of a connection comprising suchpin and box connectors may be twice that of the main portion of the bodyof the stem, said body having a transition portion between each end andthe main body portion, said transition portions each having an outerdiameter smaller than that of said ends and larger than that of saidmain portion of the body.
 10. Subject matter of claim 7 furtherdistinguished by: the length of the box connector being at least of theorder of twice the outer diameter of the connector, the length of themaximum diameter portion of the pin connector being in the range ofnearly twice to aboue seven times the outer diameter of the connector.11. An intermediate drill stem comprising an elongated, tubular, alloysteel body the main portion of which has a substantially uniform outerdiameter, the exterior surface of said main portion being a machinedsurface, said body having at least one portion located between andspaced from the ends of the body which one portion has a larger outerdiameter than said main portion of the body, said portion of largerouter diameter being formed integral with said main portion of the bodyand providing a protector against wear on the main portion of the body,the ends of said protector being tapered where they join the mainportion of the body, said body having a wall thickness of at leastfive-eighths inch in the main portion thereof, said body having ends oflarger outer diameter than the main portion of the body, the outerdiameter of said ends being substantially as large as that of saidprotector, said body having a transition portion between each end andthe main body portion, said transition portions each having an outerdiameter smaller than that of said ends and larger than that of saidmain portion of the body, a tubular alloy steel connector rod welded toeach end of said body, said connectors each having a larger outerdiameter than the end of the body to which it is welded, the weld metaloverlapping the end to build up its outer diameter to that of theconnector, a tapered elevator shoulder at each end of the body extendinginto said build up of weld metal thereon, the inner diameters of saidconnectors being equal to each other and slightly smaller than that ofthe main portion of said body, the inner diameter of said body beinguniform throughout except at the ends where the body is built up withweld metal on the inside to make the ends have the same inner diameteras the connectors adjacent the welds, one of said connectors beinginteriorly threaded at its end opposite from its welded end to provide abox at one extemity of the stem, the other of said connectors having aportion of reduced outer diameter at its end opposite from its weldedend, said portion of reduced outer diameter being threaded to provide apin at the other extemity of the stem, the maximum outer diameterportion of each of said connectors being at least 1.2 times that of saidmain portion of the body whereby the rigidity of a connection comprisingsuch pin and box connectors cay be twice that of the main portion of thebody of the stem, the length of the maximum diameter portion of the pinconnector being in the range of nearly twice to about seven times theouter diameter of the connector. the combined length of the maximumdiameter portions of the pin and box connectors being in the range offour to ten times the outer diameter of said maximum diameter portions,the length of each protector being at least of the same order ofmagnitude as the outer diameter of the protector, each said protectorhaving a diameter at least one-half inch larger than that of said mainportion of the body, said connectors and each protector body providingcentralizers for said intermediate stem, the longitudinal spacingbetween said centralizers being a maximum of 15 feet.
 12. Anintermediate drill stem comprising an elongated, tubular, steel body themain portion of which has a substantially uniform outer diameter, saidbody having a wall thickness of at least about five-eighths inch in themain portion thereof, a tubular alloy steel connector connected to eachend of said body, one of said connectors being interiorly threaded atits end opposite from its end that is connected to said body, saidinteriorly threaded end providing a box at one extremity of the stem,the other of said connectors having a portion of reduced outer diameterat its end opposite from its end that is connected to said body, saidportion of reduced outer diameter being threaded to provide a pin at theother extremity of the stem, the maximum outer diameter portion of eachof said connectors being at least 1.2 times that of said main portion ofthe body whereby the rigidity of a connection comprising such pin andbox connectors can be twice that of the main portion of the body of thestem, said connectors being long axially compared to the diameterthereof, the combined length of the maximum diameter portions of the pinand box connectors being at least four times the outer diameter of saidmaximum diameter portions, the outer surface of said main portion ofsaid body being a turned machined surface, said body having ends oflarger outer diameter than that of said main portion of the body, eachconnector being welded to one of said ends, said body having at leastone portion located between and spaced from the ends of the body whichone portion has a larger outer diameter than said main portion of thebody, said portion of larger outer diameter providing a protectoragainst wear on the main portion of the body, each said protector beinghomogeneously integral with said main portion of the body, saidprotector and main portion being one and the same single piece of metal,each said protector having an outer diameter at least one-half inchlarger than the outer diameter of the main portion of the body of thestem, the length of each protector being at least twice the outerdiameter of the connectors, said long connectors and each said protectorbeing spaced apart along the length of the stem and serving ascentralizers for said intermediate stem.
 13. Subject matter of claim 12,further distinguished by: said body having a transition portion betweeneach end and the main body portion, said transition portions each havingan outer diameter smaller than that of said ends and larger than that ofsaid main portion of the body.
 14. Subject matter of claim 12 furtherdistinguished by: the outer diameter of said ends of the body beingsubstantially as large as that of said protector, said connectors eachhaving a larger outer diameter than the end of the body to which it iswelded, the weld metal overlapping the end to build up its outerdiameter to that of the connector.
 15. Subject matter of claim 14further distinguished by: said body having a transition portion beTweeneach end and the main body portion, said transition portions each havingan outer diameter smaller than that of said ends and larger than that ofsaid main portion of the body.
 16. Subject matter of claim 14 furtherdistringuished by: said stem having an elevator shoulder at each end ofthe body at the juncture of said end and the weld, each shoulderincluding a portion of the metal of the weld and a portion of the metalof the end of the body.
 17. Subject matter of claim 16 furtherdistinguished by: said body having a transition portion between each endand the main body portion, said transition portions each having an outerdiameter smaller than that of said ends and larger than that of saidmain portion of the body.
 18. Subject matter of claim 12 furtherdistinguished by: the ends of said protector being tapered where theyjoin the main portion of the body, the longitudinal distance between theadjacent extremities of adjacent ones of said centralizers being not inexcess of 15 feet.
 19. Subject matter of claim 12, said connectors beingfree of hard facing thereabout, said protector being of smaller outerdiameter than that of the maximum outer diameter portion of saidconnectors, said protector having a band of hard facing material set inan annular groove around said protector.
 20. Subject matter of claim 12wherein said intermediate stem has an inner diameter characteristic of adrill collar and an outer diameter characteristic of drill pipe.
 21. Anintermediate drill stem comprising an elongated, tubular, steel body themain portion of which has a substantially uniform outer diameter, saidbody having ends of larger outer diameter than that of the main portionthereof, a tubular alloy steel connector connected to each end of saidbody, one of said connectors being interiorly threaded at its endopposite from its end that is connected to said body, said interiorlythreaded end providing a box at one extremity of the stem, the other ofsaid connectors having a portion of reduced outer diameter at its endopposite from its end that is connected to said body, said portion ofreduced outer diameter being threaded to provide a pin at the otherextremity of the stem, the maximum outer diameter portion of each ofsaid connectors being at least 1.2 times that of said main portion ofthe body whereby the rigidity of a connection comprising such pin andbox connectors can be twice that of the main portion of the body of thestem, each of said connectors being connected to one of said ends of thebody by added weld metal joining the connector to the end, eachconnector having a maximum outer diameter larger than the end of thebody to which it is welded, the weld metal overlapping the end to suchan extent as to build up its outer diameter to that of said maximumdiameter of the connector.
 22. Subject matter of claim 21 said stemhaving an elevator shoulder at each end of the body at the juncture ofsaid end and the weld, each shoulder including a portion of the metal ofthe weld and a portion of the metal of the end of the body. 23.Combination of claim 1 including the hereinbefore set forth invention.24. An intermediate drill stem comprising an elongated, tubular, alloysteel body the main portion of which has a substantially uniform outerdiameter, said body having ends of larger outer diameter than that ofthe main portion thereof, said main portion having a wall thickness ofat least about five-eighths inch, a tubular alloy steel connectorconnected to each end of said body, one of said connectors beinginteriorly threaded at its end opposite from its end that is connectedto said body, said interiorly threaded end providing a box at oneextremity of the stem, the other of said connectors having a portion ofreduced outer diameter at its end opposite from its end that isconnecteD to said body, said portion of reduced outer diameter beingthreaded to provide a pin at the other extremity of the stem, themaximum outer diameter portion of each of said connectors being at least1.2 times that of said main portion of the body whereby the rigidity ofa connection comprising such pin and box connectors can be twice that ofthe main portion of the body of the stem, said connectors being longaxially compared to the diameter thereof, the combined length of themaximum diameter portions of the pin and box connectors being at leastfour times the outer diameter of said maximum diameter portions, theouter surface of said main portion of said body being a turned machinedsurface, said body having ends of larger outer diameter than that ofsaid main portion of the body, each connector being homogeneouslyintegral with one of said ends of the body, each said connector and bodybeing made of one and the same piece of metal, said body having at leastone portion located between and spaced from the ends of the body whichone portion has a larger outer diameter than said main portion of thebody, said portion of larger outer diameter providing a protectoragainst wear on the main portion of the body, each said protector beinghomogeneously integral with said main portion of the body, saidprotector and main portion being one and the same single piece of metal,each said protector each having an outer diameter at least one-half inchlarger than the outer diameter of the main portion of the body of thestem, the length of each protector being at least twice the outerdiameter of the connectors, said long connectors and each said protectorbeing spaced apart along the length of the stem and serving ascentralizers for said intermediate stem.
 25. Subject matter of claim 12,said body being made of steel in the A.I.S.I. 1100 to 1,200 series.